Association of Homozygous Thrombophilia Polymorphisms and Venous Thromboembolism in Shahrekord, Iran.

BACKGROUND
Venous thromboembolism (VTE) is a major cause of mortality. Factor V Leiden (FVL), methylenetetrahydrofolate reductase (MTHFR) C677T, and prothrombin (FII) G20210A polymorphisms are the main inherited risk factors for VTE. Since evidence is limited on homozygotes, the aim of this study was to investigate the association between homozygous variants of these polymorphisms and VTE in Shahrekord, southwest Iran.


MATERIALS AND METHODS
In this case-control study, blood samples of 72 VTE patients admitted to Hajar Hospital, Shahrekord and 306 sex- and age-matched healthy volunteers as controls were taken in EDTA Vacutainers. The polymorphisms of FVL, MTHFR C677T, and FIIG20210A were investigated by PCR-RFLP. The data were analyzed by descriptive statistics and independent t-test.


RESULTS
The frequency of all homozygous polymorphisms was found to be 16.77% in patients and 4.90% in controls with a significant difference (P=0.004). Homozygous FVL mutation was more frequent in patients than in controls with no significant difference. Regarding the frequency of homozygous MTHFR C677T, a significant difference was noted between patients and controls (P=0.03). There was no significant difference in homozygous FIIG20210A and heterozygous variants of the above-mentioned polymorphisms between the patients and controls.


CONCLUSION
Homozygous MTHFR C677T polymorphism is associated with VTE in Shahrekord. Control of the acquired risk factors may be necessary in homozygous form of this polymorphism. VTE patients with this polymorphism may need to be managed differently.


INTRODUCTION
Venous thromboembolism is a disease in which both inherited and acquired factors may be involved. Although the real prevalence of VTE, consisting of deep venous thrombosis (DVT) and pulmonary embolism (PE), remains to be determined in many communities, it is known to be one of the main causes of mortality. In the United States, VTE is considered as the third leading cause of mortality and a leading cause of unpredictable deaths (1). Even the people who survive PE have a lower quality of life than healthy people (2).
Coagulation factor deficiencies, platelets abnormalities, impaired vessel wall, and coagulation inhibitors can contribute to developing thrombosis. Thrombophilia is a Moreover, the role of factor XIII and platelet glycoprotein IIb/IIIa has been recently considered in VTE (3,4). FVL is a mutation of coagulation factor V that makes FVL resistant to protein C, its inhibitor (5). MTHFR plays an important role in maintaining homocysteine level. The C677T polymorphism of MTHFR molecule makes the enzyme heat resistant and may increase serum homocysteine which is a predisposing factor for thrombosis (6). The MTHFR C677T has been reported to be associated with increased VTE in a Chinese population but some conflicting data have been reported in other ethnicities (7). The FIIG20210A polymorphism is associated with increased plasma prothrombin level and increased risk of venous thrombosis (8), and the FIIG20210A carriers are at 2-3 times higher risk for developing VTE (9,10). The frequencies of these polymorphisms vary depending on the racial origins in both normal and VTE patient populations (9)(10)(11), and the available data confirm widely variable distribution of different polymorphisms.
We have already found that PLA2 polymorphism of platelet glycoprotein IIb-IIIa is associated with increased risk of developing VTE and severity of PE (3,12). Because homozygosity in any of the polymorphisms can increase the gene products and relevant data are limited, the aim of this study was to investigate the association between homozygous variants of these mutations and VTE.

Statistical analysis
The data were analyzed by SPSS 18. Descriptive statistics were used for the demographic characteristics.
The significance of the differences in the distribution of homozygous polymorphisms between the patients and the controls was investigated by chi-square test, and P<0.05 was considered significant. Moreover, the odds ratio (OR) was used to represent the association of the polymorphisms with VTE. polymorphisms between the patients and controls. Figure   1 illustrates the PCR-RFLP products of FVL, MTHFR C677T, and FIIG20210A on polyacrylamide gel.

DISCUSSION
This study demonstrated that VTE was associated with a number of homozygous thrombophilic polymorphisms, and some of the known thrombophilic homozygous polymorphisms increased the risk of developing VTE, while others had no effect. In a study on factor XIII polymorphisms, homozygous FXIIIA-V34L was found to protect against VTE, while heterozygous FXIIIA-V34L and XIIIB-H95R had no effect (4). Besides, the frequency of coincidence of thrombophilic mutations was found to be higher in DVT patients than in PE patients and controls (14). In a study conducted in an Australian Caucasian population, 64.2% and 24.5% of studied group were homozygous and heterozygous, respectively at least for one of the inherited thrombophilia; these values are higher than our findings (15). Among the patients in our study, the most frequent homozygous polymorphism was found to be MTHFR C677T (11.11%). This polymorphism is distributed among all populations and is more frequent in some racial populations (9,10). It has been found more commonly in Australians, Europeans and Chinese than Because of the limited number of patients in our study, we could not investigate the significance of such coinheritance.
We studied a limited number of homozygous